The present invention relates to an object detector employing an infrared superconductive device, in which the location of an object is detected.
An infrared detector finds its general use in a control device for an automatic door or in a burglar alarm device. Such an infrared detector senses an object present in a specific detection area. A method for defining the detection area will be described.
As shown in FIG. 1, an infrared detector 1 is installed on the upper part of an entrance wall or on a ceiling 2, and a detection area is defined with respect to a floor 3, opposing the infrared detector 1. In this method, an object like a person 4 is detected so long as it steps into the shaded area of FIG. 1.
Further, an object detection range may be limited to a predetermined distance from the infrared detector by adjusting the sensitivity thereof. That is, the detection range reaches far by increasing the sensitivity, and is confined to a short distance by decreasing the sensitivity.
However, a problem with the prior art is that the infrared detector cannot be widely used, due to area constraints involved in its installation. Another problem is that installing the infrared detector in a high place (e.g., on a ceiling) is a difficult task, which makes it less acceptable in terms of safety and maintenance. Further, the detection range itself is not easy to control by adjusting the sensitivity of the infrared detector, resulting in frequent adjustments depending on ambient conditions like weather and needs for cooling or heating.
To overcome the above problems of the prior art, an infrared object detector shown in FIGS. 2 and 3 has been suggested. This infrared object detector is easy to install and obviates the need for additional control of the sensitivity thereof. As shown, it is comprised of a pair of light receiving elements arranged in such a way that their light receiving views intersect each other in a detection area, a pair of comparators for comparing the output levels of the pair of light receiving elements with their respective reference levels and outputting respective detection signals for an object, and a determiner for determining whether the object exists in the predetermined detection area, according to the concurrence of the detection signals.
In the conventional infrared object detector as constituted above, the detection area is defined where the light receiving views of the pair of light receiving elements intersect each other. When an object enters the detection area, both the light receiving elements concurrently produce their detection signals. Therefore, the absence or presence of the object in the detection area is determined on the basis of the concurrent detection signals.
Referring to FIGS. 2 and 3, the infrared object detector is comprised of a sensing unit 10 and a signal processing unit 20. The sensing unit 10 has light receiving windows 11a and 11b at both end portions of the front surface thereof. A detection area D is defined by the intersection of the light receiving views of the light receiving windows 11a and 11b, as shown in FIG. 2. The light receiving views of the light receiving windows 11a and 11b are defined by hoods 12a and 12b. An optical system (not shown) and infrared sensors 13a and 13b are arranged behind the hoods 12a and 12b. The outputs of the infrared sensors 13a and 13b are amplified in amplifiers 21a and 21b and transmitted to window comparators 22a and 22b, respectively. An AND circuit 23 receives the amplified outputs through the window comparators 22a and 22b, thereby producing a determination output.
The constitution of the infrared sensors 13a and 13b is illustrated in FIG. 4A. Each of the infrared sensors 13a and 13b includes a superconductive device 15 in a package 14. The output of the superconductive device 15 is impedance-transformed in a field effect transistor (FET) 16, and the impedance-transformed signal is output to the signal processing unit 20. A transparent window member 17 is provided to a light receiving aperture of the package 14, and an optical lens 18 is disposed in front of the transparent window member 17.
FIG. 4B illustrates the signal output V.sub.out of the infrared sensor 13. When an object appears in a light receiving view at the time point of t1 and disappears from the view at the time point of t2, the intensity of infrared incident light is changed, so that both outputs V.sub.out of the infrared sensors 13a and 13b are inverted with respect to the time points 1 and 2, respectively, as shown in FIG. 4B.
Referring to FIG. 5, 5A and 5B indicate the impedance-transformed outputs of the infrared sensors 13a and 13b, respectively. WA and WB indicate the outputs of the window comparators 22a and 22b, respectively. V.sub.TU and V.sub.TL indicate a high level reference potential and a low level reference potential of the window comparators 22a and 22b, respectively. As shown in FIGS. 5A and 5C, when an object is located at a short or long distance (see FIG. 3), the outputs of the window sensors 22a and 22b are not concurrently produced, while when the object exists in the detection area (medium distance), the concurrence of the outputs is obtained, as indicated by shaded portions of FIG. 5B.
Therefore, the absence or presence of the object in the detection area can be determined by the output OUT of the AND circuit 23.
Efforts have been recently expended toward applications of such an infrared object detector to such an air conditioner as a room air conditioner (RAC) or a package air conditioner (PAC), so that the location of a person present indoor is detected, thereby operating the air conditioner in an optimum state.
However, the conventional infrared object detector exhibits limitations in its application to an air conditioner, in that the two-dimensionally defined detection area is an obstacle to the three-dimensional detection of a person in consideration of the distance between the detector and the person and the degree of his movement. As a result, the air conditioner cannot be controlled properly enough to produce the optimum output.